This invention relates to thin-film superconducting junction devices.
The semiconductor junction has been exploited to produce a wide variety of devices including junction diodes, junction transistors and many others. In particular, the semiconductor junction transistor is formed by disposing in linear sequence three sections of semiconductor material that are doped to produce sequentially alternating majority carriers and that are separated by depletion layers thin by comparison with the characteristic distances for diffusion of minority carriers. In such semiconducting devices the possibility of varying dopants so that majority carriers may be either electrons or holes produces the possibility of making rectifying junctions. However, such rectification is not related inherently to transistor action, which is here defined as the production by injection into a junction of an effect that is greater in magnitude than the magnitude of the injection. In a semiconducting junction the injection is of minority carriers into the base. Thus, electrons are injected into a base formed of P material, which is material formed by doping a valence-4 semiconductor with a valence-3 dopant. Correspondingly, holes are injected into a N material which is a valence-4 semiconductor doped with a valence-5 material.
The mechanism of conduction is different in superconductors. Superconduction has been explained successfully as the collective action of paired electrons (Cooper pairs) in a single quantum state below a critical temperature. There is no equivalent to the doping of semiconductors, and no structure that exhibits a preferential direction of conduction like the junction transistor. However, there are two phenomena that can be exploited to provide transistor action in a superconducting device. One of these is the tunneling of unpaired electrons (quasiparticles) through thin insulating layers. The other is the possibility of injecting quasiparticles into a superconducting region by superconducting tunneling.
It is an object of the present invention to produce transistor action with a superconducting device.
It is a further object of the present invention to produce a measured current gain in a device made of thin films of superconductors.
Other objects will become apparent in the course of a detailed description of the invention.